The present invention relates to a drum cleaning apparatus for an electrostatic copying machine.
In an electrostatic copying machine of the dry development type, a photoconductive drum is electrostatically charged and radiated with a light image of an original document to form an electrostatic image thereon through localized photoconduction. A powdered toner substance is applied to the drum to develop the electrostatic image into a toner image which is transferred and fixed to a copy sheet to form a permanent reproduction of the original document.
However, not all of the toner substance is transferred to the copy sheet and residual amount remains. The residual toner substance must be removed prior to another copying operation in order to avoid double printing (the superimposition of an image of the previous document on that of the subsequent document).
An effective way to remove the residual toner substance and thereby clean the drum is by means of a resilient scraper blade made of rubber or the like. In order to preclude contamination of the internal components of the copying machine with the residual toner substance scraped off the drum by the scraper blade it is necessary to catch the toner substance and convey the same to a container, preferably for recycling. It has been proposed in the prior art to provide a roller below the scraper blade. The roller is driven in such a direction as to carry the toner substance which falls thereon from the scraper blade to a container. In order to be effective, the scraper blade must be disposed above the axis of the drum and the roller must be below the axis of the drum. Whereas this type of arrangement is marginally effective, it is inadequate when the amount of toner substance removed by the scraper blade is greater than a certain value. More specifically, although a portion of the removed toner substance is carried to the container by the roller another portion of the removed toner substance spills off the roller onto operating parts of the copying machine.
Two expedients have been attempted in the prior art in order to overcome this problem. As the first, a bias voltage has been applied to the roller which attracts the toner particles and prevents the same from spilling off the roller. However, unless the bias voltage is high enough to cause deterioration of the toner particles and make the same unsuitable for recycling, this first expedient is ineffective.
The second prior art expedient is to make the roller larger in diameter, thereby providing a larger surface area for the toner substance falling from the scraper blade. Whereas this expedient does improve the effectiveness somewhat, it is still inadequate and merely contributes to an overall increase in size of the copying machine.